The public switched telephone network (PSTN) was originally a network of public circuit-switched telephone links. More recently, packet-based networks, such as Internet Protocol (IP) networks, are being used as alternatives to conventional PSTN networks. Voice over IP (VoIP), for example, is commonly used to transmit voice over IP networks.
One protocol frequently used with VoIP calls is the so-called Session Initiation Protocol (SIP). SIP is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. It can be used to create two-party, multiparty, or multicast calls.
Typically, users of a telephone system, such as a VoIP system, subscribe to telephone services that have a number of user-configurable options. For example, a service may allow subscribers to turn call-forwarding on or off or use distinctive ring sounds for long distance calls. One way to allow users to modify such features is through “star codes.” With star codes, a user may dial predetermined codes, typically beginning with a preselected character (e.g., a “*”), to modify features. For example, a user may dial “*70” to disable call waiting.
In operation, star codes may be transmitted by the phone to a switching facility used in the telephone infrastructure (e.g., central office or SIP proxy server). The switching facility intercepts the star code and updates the appropriate feature of the user's account.
One problem with star codes is that it can be difficult for the average user to remember all of the codes. Some providers give users the ability to configure their account features through a separate web interface. This option, however, requires that the user have a web browser available.